Bottom brick for ingot molds

ABSTRACT

The bottom plug for ingot molds is frusto conical and at least the upper portion thereof, facing the metal, is formed of an unburned mixture of at least about 92 percent of fine grained refractory material and not more than 8 percent of an organic binder. The plug may have a lower less heat resistant layer and may also have a thin top covering layer or coating of a highly heat resistant metal oxide or of sheet metal and may have an upper surface shape e.g. disked to prevent splashing of the molten metal as it is poured into the mold.

United States Patent Loiberg et al. [451 Aug. 8, 1972 [54] BOTTOM BRICK FOR INGOT MOLDS [72] Inventors: Jan Anders Stensson Lofberg; Per 7 [56] References C'ted gavilson, both of Sandviken, UNITED STATES PATENTS we 4 3,123,878 3/1964 Davidson ..l64/6 Asslgneer g g fl J g Aktlebolag, 3,146,504 9/1964 Hansen ..249/204 an v1 en, we en Primary Examiner.l. Spencer Overholser [22] 1970 Assistant Examiner-Ben D. Tobor [21] Appl. No.: 91,562 Attorney-Pierce, Schefi'ler & Parker Related US. Application Data 57 T C Continuation of 707,176 The bottom plug for ingot molds is frusto conical and 1968, abandonedat least the upper portion thereof, facing the metal. is formed of an unburned mixture of at least about 92 Forelgn Application Priority Data percent of fine grained refractory material and not June 22,1964 Sweden ..7579/64 mam" f 335;12 :21 gggg 21 2;; :23 5135 Sept. 18, 1964 Sweden ...ll205/64 also have a thin p covering layer or coating of a highly heat resistant metal oxide or of sheet metal and 'T"" 106/ may have an upper surface shape e.g. disked to I I n I I u u c I o n a 0 I o n n v I e v I u 0 I o 0 a o n o e o o e o I n 4 n I o u II I h f th t 9 d [58] Field of Search ..249/174, 204; 164/344, 406, mg 0 e me pure 3 Claims, 4 Drawing Figures BOTTOM BRICK FOR lNGOT MOLDS This is a continuation of application Ser. No. 707, 176, filed Feb. 21, 1968, now abandoned.

The invention pertains to improvements in bottom bricks or bottom plugs for ingot molds. In such molds there is a hole in the bottom to facilitate stripping of the ingot from the mold. This hole is closed during the casting by a brick forming a bottom plug. The invention is also useful in bricks for making a supply channel for pouring the metal into the mold.

Previous bottom plugs have been made from chamotte which has certain disadvantages in that the plugs have to be burned during manufacture which causes changes in size and shape and furthermore they are liable to be eroded by the stream of metal poured into the mold so that particles of the plug mix with the cast metal. The chamotte plug also tends to adhere to the ingot after freezing of the metal.

It has been tried to use plugs of metal, for instance cast iron, in order to solve these problems but inspite of their technical advantages such plugs are too expensive for use on a large scale.

The present invention provides a bottom plug which eliminates the disadvantages of previous plugs and which is cheap to manufacture. The plugs according to the invention are made of refractory fine grained material mixed with a binder and are formed without burning or sintering. Thus a plug is obtained which does not change its shape or size after forming and which is resistant to erosion from the metal stream. It further does not easily adhere to the ingot. It has a high mechanical strength and is tight and provides a smooth surface facing the ingot.

The bottom bricks or plugs according to the invention are characterized in that at least on the side which faces the ingot they consist essentially of a composition of fine grained refractory material and a binder, preferably an organic binder such as a resin glue. The

in order to avoid porosity which would permit intrusion of molten metal between the grains thereby causing the plug to adhere to the ingot. The material can be acid, neutral or basic and can consist of natural sand, quartz, dolomite, olivine or similar material.

The refractory material should usually have a grain size such that 80 100 percent passes a screen of 18 mesh US standard (opening 1.0 mm). The particle size distribution of the material below this size can vary. It is possible to use materials a substantial part of which pass a screen of 200 mesh (0.075 mm) but in practice materials are often used 50 percent or more and often 75 percent or more of which remains on a screen of 200 mesh. Satisfactory results have been obtained with sands 50 percent or more of which lie between the limits 200 30 mesh (0.075 0.6 mm). Besides the said fine grained refractory material the composition can contain a fibrous refractory material such as asbestos, rock wool or the like in a minor quantity, for instance up to 5 percent.

quantity of the binder is 0.5 8 percent by weight of the composition, the bricks having a tight structure and a smooth surface facing the cast metal.

Other details and advantages of the invention appear from the following description and drawings in which:

FIG. 1 is a vertical section of an ingot mold with a partial section of a bottom plug according tothe invention, and

FIGS. 2 4 are alternative embodiments on a larger scale than in FIG. 1 of bottom plugs according to the invention.

The ingot mold 10 in FIG. 1 has a bottom hole 11 with a frusto conical, downwardly tapering side wall. The purpose of this hole in the ingot mold is to facilitate the stripping of the ingot from the mold after casting. During casting the hole is closed by a matching plug 12. This plug is, as stated above, made of a composition consisting of fine grained refractory material and a binder. The plug 12 illustrated in FIG. 1 is homogeneous while the plug 15 in FIG. 2 is composed of two layers both of which contain fine grained refractory material, the material in the top layer being more heat resistant that the material in the bottom layer.

In the plug 12 in FIG. 1 the refractory material preferably should have an average grain size of 0.01

The binder can in certain cases be inorganic and consist of, for instance, water glass but the preferred binders are organic, usually a resin glue, often synthetic. Furan resin glue with a hardener such as phosphoric acid has been found especially suitable because this kind of glue is self-hardening at room temperature which makes heating of the fonned plug superfluous and makes it possible to obtain a high accuracy in the size and shape of the plug. The quantity of binder should be 0.5 8 percent by weight. The most suitable range is 0.5 4.5 percent, preferably 1 3 percent of the weight of the refractory-binder composition.

A brick according to the invention thus contains in the main the following weight ratio of ingredients:

Binder Refractory material Of the refractory material a small quantity, for instance up to 5 percent by weight of the composition, can be a fibrous refractory material as mentioned above. A minor quantity of the refractory material for instance up-to 2 or 3 percent of the composition, can be substituted by e. g. organic material as paper pulp or the like.

After mixing the ingredients and molding the brick can be rendered more compact by vibration, ramming and/or pressing, for instance in a. hydraulic pressing machine. In certain cases a slight heating is useful in order to cause the glue to harden but this is not necessary if the binder is self-hardening at room temperature as is the furan resin glue.

,As an example of a bottom plug or other bottom brick of the homogeneous type shown in FIG. 1 can be mentioned a brick containing 2 percent by weight of furan resin glue, the remainder being lake sand. The sand contains about 90% SiO and has an average grain size of about 0.27 mm.

In the homogeneous plug 12 a refractory material with relatively high heat resistance is required, for instance sand with a high content of silica, suitably above percent, or olivine sand. The heat resistance of a quartzite sand increases with the SiO content.

The plug 15 in FIG. 2 consists of two layers, the top layer 13 providing contact with the molten metal and the bottom layer 14 providing the necessary mechanical strength. The top or contact layer can suitably consist of a refractory material with very high heat re sistance and also having other desirable properties. It should be resistant to the stream of molten cast metal and it should preferably not be wetted by the cast metal in order to avoid adhesion of the plug to the ingot. Such adhesion can be caused by sintering of the material to the ingot. The average grain size and the binder content can suitably. be the same as for the plug 12 described above.

Since the top layer 13 is comparatively thin in comparison with the bottom layer 14 it is economically possible to form it of refractory materials of higher quality and at the same time more expensive than the materials which are suitable for the plug 12. Layer 13 can for instance be formed of zirconium sand or oxides of the metals zirconium, aluminum, magnesium and chromium or other materials having the said desired properties. Sometimes burned or unburned dolomite or limestone can be used. The material in this top layer 13 should have a higher heat resistance than common quartz sand and a sintering temperature above the temperature of the cast metal which usually is steel, suitably above 1,5 C. Zirconium sand has a sintering temperature of about 1,800 C, while quartz sand has a sintering temperature of about l,400 C.

The bottom or supporting layer 14 can be made of a cheaper refractory material with a lower heat resistance as for instance quartzite or olivine sand. Also dressed ore, carbon black, graphite, silicon carbide, crushed light concrete and sands containing comparatively little silica such as foundry sand, lake sand or other similar sand can be used. Because of the lower heat resistance some sintering may occur in this layer but this can be permitted. The grain sizes and binder content should also for this layer suitably be approximately the same as earlier defined for the plug 12. The binder content can be somewhat higher, up to 6 percent.

The top layer 13 should be as thin as possible without risking the desired function. A thickness of l 20 mm, often 3 mm, has been found suitable. The ingredients for the two layers are mixed and deposited separately, after which the plug is molded and can be compressed by vibrating, ramming and/or pressing, as above mentioned.

A plug consisting of two layers may have the following distribution of material in percent by weight:

3 7 percent, preferably 4 6 percent of zirconium sand forming the top layer.

90 94 percent, preferably 91 93 percent of a less heat resistant refractory material, forming the bottom layer.

1 4.5 percent, preferably 2 4 percent of a resin glue.

The binder content can be equal in both layers or somewhat higher in the bottom layer.

The layers 13 and 14 need not be sharply distinguished from each other but can merge gradually. Likewise there can be more than two layers, the plug consisting of a number of successive layers with gradually changing properties. In the plug in FIG. 2 it is, for instance, possible to mold the plug with two layers, the top layer being more heat resistant, and then to provide an additional thin layer on top of the plug by flame spraying as below described.

An important reason for having the plug as compact as possible is that it should have a good heat conductive ability. If the heat is lead away rapidly at the bottom of the ingot the freezing center lies at a low level in the ingot and this improves the sinking of the sink head. The plug according to the invention is advantageous in this regard because the cheaper sand qualities employed in the bottom layer 14 generally have a better heat conduction than the more expensive materials in the top layer 13. In order to improve the heat conduction the plug can be provided with recesses or inserted bodies or layers with good heat conduction (not shown).

The plug according to the invention is manufactured without burning or sintering which is a substantial advantage in comparison with earlier known plugs of burnt brick material because the manufacturing tolerances can be held within narrow limits. With some binders a slight heating may be necessary, which, however, does not substantially affect the shape of the plug. If a binder is employed which is self-hardening at room temperature, such as furan resin glue, no heating at all is necessary.

In both embodiments illustrated in FIGS. 1 and 2 the top surface of the plug can be covered by a thin layer of some heat resistant oxide which can be applied, for instance by flame spraying. This thin layer can consist of oxide of zirconium or oxide of chromium or some other similar refractory oxide or other substance having a high heat resistance. In this way a higher resistance against erosion by the metal stream and a diminishing of the tendency of the brick to adhere to the cast metal can be obtained.

Another way of improving the erosion resistance of the plug is illustrated in FIG. 3. The upper surface of the plug 20 is covered by a metal sheet 21 which can be anchored to the plug as by means of nails 22. In casting steel a steel sheet of for instance 0.5 mm thickness can be used. The sheet provides a temporary protection during the beginning of the casting after which it melts and mixes with the ingot. This embodiment can be used for the homogeneous plug in FIG. 1 as well as for the two layer plug in FIG. 2. The metal sheet may be extended upwardly by a flange 23 in order to prevent splashing and wave formation in the molten metal during the beginning of the casting or this flange may be omitted. In FIG. 3 is shown also an upward depression 24 in the bottom of the plug in order to save material. The mechanical strength of the plug with this depression is sufficient because of the arch effect against the inclined edge. Such depressions can be used also in the other embodiments or omitted.

In FIG. 4 is shown a plug 30 which has a depression 31 in its top surface in order to eliminate splashing and wave formation in the metal thereby diminishing the erosion of the mold by the violent sideward flow which occurs when the stream of metal reaches the bottom of the mold. The surface of the ingot is also improved if the waves and splashing of the metal is reduced as much as possible. The plug in FIG. 4 can be made either of a homogeneous material as in FIG. 1 or in layers as in FIG. 2, and it can be covered by a protective metal sheet as shown in FIG. 3 or coated with a thin top layer as described above but not illustrated.

In order to determine the ability of the plug to resist erosion by the stream of molten metal comparative tests have been made with plugs of the previous construction (chamotte plugs) and plugs according to the invention. A radioactive tracing substance was incorporated into the plugs. After casting the inclusions in the ingot containing the radioactive substance were registered photographically and it was found that the number of inclusions caused by the plug was only a third as great for a plug according to the invention compared with a chamotte plug.

The invention has been described for a bottom plug of an ingot mold and has its main use for such plugs. The invention can, however, be used also for bricks which are used for supply channels to ingot molds which are cast from the bottom, the internal surfaces of such bricks being exposed to the molten metal under conditions which in, essential respects are similar to the conditions of the above described bottom plugs used in ingot molds.

We claim:

1. Bottom plug for an ingot mold for casting metals, said plug having a high resistance to erosion and a low tendency to adhere to such cast metal, said plug consisting of an unburned compact having a composition consisting of (a) fine grained inorganic refractory material of the group consisting of sand of dolomite, olivine, zirconium, alumina, chromium oxide, and sand having a silica content in excess of percent as quartz sand, said refractory material having an average grain size of from 0.0l-l.0 mm, bonded together into a unitary body by means of (b) an organic binder in the amount of from 0.5-8.0 percent by weight based on the weight of the composition, said organic binder being the only organic constituent of said composition, the plug having a compact and impervious structure and a smooth surface facing the cast metal.

2. The ingot mold bottom plug defined in claim 1, in which the refractory material component of the composition consists essentially of particulate olivine and the organic binder component of the composition consists essentially of a resin glue.

3. The ingot mold bottom plug defined in claim 1, in which the refractory material component of the composition consists essentially of sand containing in excess of 80 percent Si0 by weight, and the organic binder component of the composition consists essentially of furan resin glue, said organic binder constituting from about 2 percent to about 4 percent by weight of the total composition.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,682,435 I August 8, 1972 Patent No. Dated Jan Anders Stensson Lofberg et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet item I73] should read Sandvikens Jernverks Aktiebolag,

Sandviken, Sweden Signed and Sealed this Seventeenth Day of May 1977 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflatents and Trademarks (0/31, M y u I CREE iLFiLCfi-rTiL OF C RRECTIQN Patent Nu 3; 35 Dated August 97 Inve:.cor.(s) JAN ANDERS STENSSON LOFBERG and PER DAVIDSON r z is certified that error'appears in the move-identified peter: an; am: Said Letters larenc are hereby corrected as shown below:

.In thea-ss1 ghe"s name fch 'ange "JERNVEKS" to JERNVERKS" .Signd end sealed this 12th dy of Deeember'l972. 4

(sEAmf Attest'z- I EDWARD- M.FLETCI+IE'R,URQ- 'ffj 1 l ROBERT .GOTTSCHALK [Attesting Offieer 'J Qommissioner of Patent: 

1. Bottom plug for an ingot mold for casting metals, said plug havinG a high resistance to erosion and a low tendency to adhere to such cast metal, said plug consisting of an unburned compact having a composition consisting of (a) fine grained inorganic refractory material of the group consisting of sand of dolomite, olivine, zirconium, alumina, chromium oxide, and sand having a silica content in excess of 80 percent as quartz sand, said refractory material having an average grain size of from 0.011.0 mm, bonded together into a unitary body by means of (b) an organic binder in the amount of from 0.5-8.0 percent by weight based on the weight of the composition, said organic binder being the only organic constituent of said composition, the plug having a compact and impervious structure and a smooth surface facing the cast metal.
 2. The ingot mold bottom plug defined in claim 1, in which the refractory material component of the composition consists essentially of particulate olivine and the organic binder component of the composition consists essentially of a resin glue.
 3. The ingot mold bottom plug defined in claim 1, in which the refractory material component of the composition consists essentially of sand containing in excess of 80 percent SiO2 by weight, and the organic binder component of the composition consists essentially of furan resin glue, said organic binder constituting from about 2 percent to about 4 percent by weight of the total composition. 